Pulse wave detection device, biological information measurement device, and control method for pulse wave detection device

ABSTRACT

A pulse wave detecting device includes a sensor section and a control unit. The sensor section is rotatable about a first axis and is rotatable about a second axis. The control unit determines a rotation angle about the first axis, and determines a rotation angle about the second axis in a state where a pitch angle of the sensor section is controlled to the optimal pitch angle. Then, in a state where the sensor section is controlled to the optimal roll angle and the optimal pitch angle, the sensor section is pressed against the body surface, and a pulse wave is detected in this state based on pressure signals detected by pressure detecting elements, and vital information is calculated based on the detected pulse wave.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT application No. PCT/JP2017/014748, which was filed on Apr. 11, 2017 based on Japanese Patent Application (No. 2016-082066) filed on Apr. 15, 2016, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a pulse wave detecting device, a vital information measuring device, a method for controlling a pulse wave detecting device, and a control program for a pulse wave detecting device.

There is a known vital information measuring device capable of measuring vital information such as the pulse, the heart rate or the blood pressure using information detected by a pressure sensor set in contact with a surface of a living body portion where an artery such as the radial artery of the wrist passes (see Patent Literatures 1 and 2).

Patent Literature 1 discloses a vital information measuring device including a drive section that rotates a pressure sensor including a plurality of element rows each including a plurality of pressure detecting elements about an axis extending in a direction perpendicular to an arrangement direction of the plural element rows (i.e., a direction perpendicular to an artery). In this vital information measuring device, maximum amplitude values of pulse waves detected by the respective plural element rows are compared with one another to rotate the pressure sensor in such a manner that the amplitude values accord with one another.

Patent Literature 2 describes a vital information measuring device including a mechanism for rotating a pressure sensor about an axis extending in a direction along an artery.

Patent Literature 1: Japanese Patent Publication No. H01-288228

Patent Literature 2: Japanese Patent Publication No. H06-507563

SUMMARY OF THE INVENTION

In the vital information measuring device described in Patent Literature 1, since the pressure sensor can be rotated about an axis extending in the direction perpendicular to an artery, an effect of improving pulse wave detection accuracy can be expected.

A hard tissue such as a bone or a tendon is present in the vicinity of the artery, however, and there is a possibility that pressure signals detected by the plural element rows may include a large number of signals according with a pressure from such a hard tissue. In order to accurately detect a pulse wave caused in the artery, it is preferable that the pressure signals are detected by the plural element rows with the influence of the pressure from a bone or a tendon excluded as much as possible. Patent Literature 1 does not, however, take the influence of the pressure from a hard tissue such as a bone or a tendon into consideration.

In the vital information measuring device described in Patent Literature 2, the pressure sensor can be rotated about an axis extending in a direction along an artery. The rotation of the pressure sensor is, however, performed for releasing a pressure applied from the wrist, and the rotation is not electrically performed.

In other words, in the vital information measuring device described in Patent Literature 2, a manner of holding the pressure sensor above an artery cannot be electrically controlled, and it is difficult to improve the pulse wave detection accuracy.

The present invention was devised in consideration of the above-described circumstances, and an object is to provide a pulse wave detecting device capable of improving pulse wave detection accuracy by flexibly changing a pressing state, toward a body surface, of a sensor section pressed against the body surface for use, a vital information measuring device, a control method for a pulse wave detecting device, and a control program for a pulse wave detecting device.

The pulse wave detecting device of the present invention includes: a sensor section in which a plurality of element rows each including a plurality of pressure detecting elements arranged in a first direction are arranged in a direction perpendicular to the first direction; a pressing section that presses the sensor section against a body surface of a living body in a state where the first direction crosses a direction of extending an artery below the body surface; a rotation drive section that rotates the sensor section about each of two axes perpendicular to a pressing direction of the pressing section, the two axes being a first axis extending in the first direction and a second axis perpendicular to the first direction; a storage control section that stores, in a storage medium, pressure signals detected by the pressure detecting elements in a state where a first rotation angle of the sensor section about the first axis is controlled to a first value, a second rotation angle of the sensor section about the second axis is controlled to a second value, and the sensor section is pressed against the body surface by the pressing section; and a rotation angle determining section that determines the first value based on the pressure signals detected by the pressure detecting elements during increase of a pressing force applied to the sensor section against the body surface by the pressing section, controls the first rotation angle to the determined first value using the rotation drive section, and determines the second value based on DC components of the pressure signals detected by the pressure detecting elements in a state where the pressing force is further increased from the thus controlled state.

The vital information measuring device of the present invention includes: the pulse wave detecting device; and a vital information calculating section that calculates vital information based on the pressure signals stored in the storage medium.

The method for controlling a pulse wave detecting device of the present invention is a method for controlling a pulse wave detecting device including: a sensor section in which a plurality of element rows each including a plurality of pressure detecting elements arranged in a first direction are arranged in a direction perpendicular to the first direction; a pressing section that presses the sensor section against a body surface of a living body in a state where the first direction crosses a direction of extending an artery below the body surface; and a rotation drive section that rotates the sensor section about each of two axes perpendicular to a pressing direction of the pressing section, the two axes being a first axis extending in the first direction and a second axis perpendicular to the first direction, and the method includes: a storage control step of storing, in a storage medium, pressure signals detected by the pressure detecting elements in a state where a first rotation angle of the sensor section about the first axis is controlled to a first value, a second rotation angle of the sensor section about the second axis is controlled to a second value, and the sensor section is pressed against the body surface by the pressing section; and a rotation angle determining step of determining the first value based on the pressure signals detected by the pressure detecting elements during increase of a pressing force applied to the sensor section against the body surface by the pressing section, controlling the first rotation angle to the determined first value using the rotation drive section, and determining the second value based on DC components of the pressure signals detected by the pressure detecting elements in a state where the pressing force is further increased from the thus controlled state.

The control program for a pulse wave detecting device of the present invention is a control program for a pulse wave detecting device including: a sensor section in which a plurality of element rows each including a plurality of pressure detecting elements arranged in a first direction are arranged in a direction perpendicular to the first direction; a pressing section that presses the sensor section against a body surface of a living body in a state where the first direction crosses a direction of extending an artery below the body surface; and a rotation drive section that rotates the sensor section about each of two axes perpendicular to a pressing direction of the pressing section, the two axes being a first axis extending in the first direction and a second axis perpendicular to the first direction, and the program causes a computer to execute: a storage control step of storing, in a storage medium, pressure signals detected by the pressure detecting elements in a state where a first rotation angle of the sensor section about the first axis is controlled to a first value, a second rotation angle of the sensor section about the second axis is controlled to a second value, and the sensor section is pressed against the body surface by the pressing section; and a rotation angle determining step of determining the first value based on the pressure signals detected by the pressure detecting elements during increase of a pressing force applied to the sensor section against the body surface by the pressing section, controlling the first rotation angle to the determined first value using the rotation drive section, and determining the second value based on DC components of the pressure signals detected by the pressure detecting elements in a state where the pressing force is further increased from the thus controlled state.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating the external structure of a pulse wave detection unit 100 of a vital information measuring device according to one embodiment of the present invention.

FIG. 2 is an enlarged view of the pulse wave detection unit 100 of FIG. 1.

FIG. 3 is a diagram, taken from a side of the elbow of a user, of the pulse wave detection unit 100 in a worn state illustrated in FIG. 1.

FIG. 4 is a diagram, taken from a side of a portion in contact with the wrist, of the pulse wave detection unit 100 in the worn state illustrated in FIG. 1.

FIG. 5 is a diagram illustrating a block structure of the vital information measuring device of the present embodiment.

FIG. 6 is a flowchart used for explaining an operation in a continuous blood pressure measurement mode of the vital information measuring device of the present embodiment.

FIG. 7 is a flowchart used for explaining details of step S3 of FIG. 6.

FIG. 8 is a diagram illustrating change in a pressure signal detected by a target element positioned above the radial artery in a selected element row selected in step S38 of FIG. 7.

FIG. 9 is a flowchart used for explaining details of step S5 of FIG. 6.

FIGS. 10A to 10C are diagrams illustrating states where a roll angle of the pulse wave detection unit 100 of FIG. 1 is controlled to three values.

FIG. 11 is a graph illustrating a relationship between a DC level of a pressure signal detected by each pressure detecting element of the selected element row in a state where the roll angle is controlled as illustrated in FIGS. 10A to 10C and the position of the pressure detecting element.

FIG. 12 is a flowchart used for explaining a modification of detailed processing of step S5 of FIG. 6.

DETAILED DESCRIPTION OF EXEMPLIFIED EMBODIMENT

An embodiment of the present invention will now be described with reference to the accompanying drawings.

FIG. 1 is a schematic diagram illustrating an external structure of a pulse wave detection unit 100 of a vital information measuring device according to one embodiment of the present invention. The vital information measuring device of the present embodiment is used while worn, with a band not shown, on a living body portion (the left wrist of a user in an exemplified case of FIG. 1) in which an artery to be measured for vital information (the radial artery T in the exemplified case of FIG. 1) is present.

FIG. 2 is an enlarged view of the pulse wave detection unit 100 of FIG. 1. FIG. 3 is a diagram, taken from a side of the elbow of the user, of the pulse wave detection unit 100 in a worn state illustrated in FIG. 1. FIG. 4 is a diagram, taken from a side of a portion in contact with the wrist, of the pulse wave detection unit 100 in the worn state illustrated in FIG. 1. It is noted that FIGS. 1 to 4 merely schematically illustrate the pulse wave detection unit 100, and do not limit dimensions and arrangement of respective components.

The pulse wave detection unit 100 includes a housing 1 including an air bag 2 therein, a plate section 3 corresponding to a plate-shaped member fixed on the air bag 3, a rotation section 5 supported on a biaxial rotation mechanism 5 a rotatably against the plate section 3 around each of two axes, and a sensor section 6 provided on a surface of the rotation section 5 on the opposite side from the plate section 3.

The air bag 2 functions, in a state where the pulse wave detection unit 100 is worn on the wrist as illustrated in FIG. 1, as a pressing section for pressing a pressing surface 6 b of the sensor section 6 against the body surface of a living body portion (the wrist). The pressing section can be any mechanism as long as it can press the sensor section 6 against the artery, and is not limited to one using an air bag.

The air bag 2 is controlled by a pump not shown for the amount of air held therein to move the plate section 3 fixed on the air bag 2 in a direction vertical to the surface of the plate section 3 (the surface on the side of the rotation section 5).

In the worn state illustrated in FIG. 1, the pressing surface 6 b of the sensor section 6 included in the pulse wave detection unit 100 is in contact with the skin of the wrist of the user. In this state, the amount of air injected into the air bag 2 is increased to increase the internal pressure of the air bag 2, and hence the sensor section 6 is pressed against the body surface. Hereinafter, the description is made on the assumption that a pressing force applied by the sensor section 6 to the body surface is equivalent to the internal pressure of the air bag 2.

As illustrated in FIG. 4, the sensor section 6 includes an element row 60 including a plurality of pressure detecting elements 6 a arranged in a direction B corresponding to a first direction, and an element row 70 including a plurality of pressure detecting elements 7 a arranged in the direction B. The element row 60 and the element row 70 are arranged in a direction A perpendicular to the direction B. In the state where the pulse wave detection unit 100 is worn on the wrist, the element row 60 is disposed on a peripheral side, and the element row 70 is disposed on a center side.

Every pressure detecting element 6 a forms a pair with a pressure detecting element 7 a disposed in the same position in the direction B, and a plurality of such pairs are arranged in the direction B in the sensor section 6. Each of the pressure detecting elements 6 a and the pressure detecting elements 7 a is any of a strain gauge resistance element, a semiconductor piezoresistance element and an electrostatic capacitance element.

The respective pressure detecting elements included in the element row 60 and the element row 70 are formed on the same plane surface, and the plane surface is protected by a protection member of a resin or the like. The plane surface having the pressure detecting elements thereon and the surface of the protection member protecting the plane surface are parallel to each other, and the surface of the protection member forms the pressing surface 6 b.

Each of the pressure detecting elements 6 a (7 a) can detect a pressure vibration wave generated in the radial artery T and transmitted to the skin, namely, a pulse wave, when pressed against the radial artery T in such a manner that the arrangement direction crosses the radial artery T (at substantially right angles).

A distance in the arrangement direction between the pressure detecting elements 6 a (7 a) is set to be so sufficiently small that a necessary and sufficient number of elements can be disposed above the radial artery T. A length of the arrangement of the pressure detecting elements 6 a (7 a) is set to be larger than the diameter of the radial artery T by a necessary and sufficient size.

As illustrated in FIG. 4, the biaxial rotation mechanism 5 a is a mechanism for rotating the rotation section 5 around each of a first axis X and a second axis Y, that is, two axes perpendicular to a pressing direction of the plate section 3 by the air bag 2.

The biaxial rotation mechanism 5 a is rotatively driven by a rotation drive section 10 described later, so as to rotate the rotation section 5 around each of the first axis X and the second axis Y set on the surface of the plate section 3 to be perpendicular to each other.

The first axis X is an axis extending in the arrangement direction of the pressure detecting elements in the element row 60 or the element row 70 (the direction B). The first axis X is set between (in the exemplified case of FIG. 4, in the center between) the element row 60 and the element row 70 in the exemplified case of FIG. 4. The first axis X is in an arbitrary position in the direction A.

The second axis Y is an axis extending in the arrangement direction of the element row 60 and the element row 70 (the direction A). The second axis Y is set on a straight line equally dividing the element row 60 and the element row 70 in the exemplified case of FIG. 4. The second axis Y is in an arbitrary position in the direction B.

When the rotation section 5 is rotated around the first axis X, the sensor section 6 is rotated about the first axis X. Besides, when the rotation section 5 is rotated around the second axis Y, the sensor section 6 is rotated about the second axis Y.

Hereinafter, the rotation of the sensor section 6 about the first axis X is designated as pitch rotation. Besides, a rotation angle of the sensor section 6 about the first axis X is designated as a pitch angle. Furthermore, the rotation of the sensor section 6 about the second axis Y is designated as roll rotation. Besides, a rotation angle of the sensor section 6 about the second axis Y is designated as a roll angle.

The pitch angle is defined by an angle between a plane vertical to the pressing direction and the pressing surface 6 b. In a state where the pressing surface 6 b is vertical to the pressing direction, the pitch angle is 0 (zero) degree. It is assumed that a pitch angle obtained by pitch-rotating the sensor section 6 from this state to one direction (a positive direction) out of rotatable directions has a positive value, and that a pitch angle obtained by pitch-rotating the sensor section 6 in an opposite direction to the one direction (a negative direction) has a negative value.

Hereinafter, a direction of rotating the sensor section 6 from the state of the pitch angle of 0 (zero) degree in a direction in which the element row 60 comes closer to the body surface (a counterclockwise direction in FIG. 1) is defined as the positive direction of the pitch rotation, and a direction of rotating the sensor section 6 in a direction in which the element row 60 comes away from the body surface (a clockwise direction in FIG. 1) is defined as the negative direction of the pitch rotation.

The roll angle is defined by an angle between the plane vertical to the pressing direction and the pressing surface 6 b. In a state where the pressing surface 6 b is vertical to the pressing direction, the roll angle is 0 (zero) degree. It is assumed that a roll angle obtained by roll-rotating the sensor section 6 from this state to one direction (a positive direction) out of rotatable directions has a positive value, and that a roll angle obtained by roll-rotating the sensor section 6 in an opposite direction to the one direction (a negative direction) has a negative value.

Hereinafter, a direction of rotating the sensor section 6 from the state of the roll angle of 0 (zero) degree in the counterclockwise direction in FIG. 3 is defined as the positive direction of the roll rotation, and a direction of rotating the sensor section 6 from the state of the roll angle of 0 (zero) degree in the clockwise direction is defined as the negative direction of the roll rotation.

Each of the pitch angle and the roll angle can be controlled to a plurality of values.

FIG. 5 is a diagram illustrating a block structure of the vital information measuring device of the present embodiment excluding the pulse wave detection unit 100.

The vital information measuring device includes the pulse wave detection unit 100, the rotation drive section 10, an air bag drive section 11, a control unit 12 for integrally controlling the whole device, a display section 13, an operation section 14 and a memory 15.

The sensor section 6 of the pulse wave detection unit 100 is provided with a temperature detecting section 7. The temperature detecting section 7 detects a temperature in the vicinity of the pressure detecting elements 6 a and 7 a, and inputs the thus detected temperature information to the control unit 12.

The rotation drive section 10 is an actuator for driving the biaxial rotation mechanism 5 a of the pulse wave detection unit 100. The rotation drive section 10 drives the biaxial rotation mechanism 5 a in accordance with an instruction issued by the control unit 12, so as to rotate the sensor section 6 about the first axis X or rotate the sensor section 6 about the second axis Y.

The air bag drive section 11 includes a pump or the like, and controls the amount of air injected into the air bag 2 (the internal pressure of the air bag 2) in accordance with an instruction issued by the control unit 12.

The display section 13 is used for displaying various information including vital information, and includes, for example, a liquid crystal display or the like.

The operation section 14 is an interface for inputting an instruction signal to the control unit 12, and includes a button and the like for instructing start of various operations including measurement of vital information.

The memory 15 is a storage medium for storing a pressure signal detected by the sensor section 6 to be used for calculation of vital information and various information including the thus calculated vital information, and includes, for example, a flash memory or the like. The memory 15 may be a removable one.

The control unit 12 mainly includes a processor, and includes a ROM (read only memory) storing programs or the like to be executed by the processor, a RAM (random access memory) used as a work memory, and the like.

The programs include a control program. The ROM is a non-transitory storage medium from which a computer can read a program. The program stored in the ROM may be one downloaded from another equipment through a network to be stored therein.

The control unit 12 has the following functions through execution, by the processor, of the programs including the control program:

The control unit 12 controls the air bag drive section 11 for adjusting the amount of air held in the air bag 2, and thus, controls the pressing force applied by the sensor section 6 to the wrist. The control unit 12 thus functions as a pressing force control section.

The control unit 12 controls the rotation drive section 10 to rotate the sensor section 6, and thus, controls the pitch angle and the roll angle of the sensor section 6. The control unit 12 thus functions as a rotation control section.

The control unit 12 sets, on the basis of a temperature detected by the temperature detecting section 7, a reference level of a pressure signal (an output signal) detected by each of the pressure detecting elements 6 a and 7 a. Owing to the setting of the reference level, the level of the pressure signal detected by each of the pressure detecting elements 6 a and 7 a can be processed as a value based on the set reference level. The control unit 12 thus functions as a reference level setting section.

The control unit 12 controls the pitch angle of the sensor section 6 to a first value, controls the roll angle of the sensor section 6 to a second value, and stores, in the memory 15, a pressure signal detected by a pressure detecting element selected from the sensor section 6 in a state where the sensor section 6 is pressed against the body surface by the air bag 2 (which state is hereinafter referred to as the pulse wave measurement state). The control unit 12 thus functions as a storage control section.

The control unit 12 calculates vital information based on pressure signals detected in the pulse wave measurement state and stored in the memory 15, and stores the calculated vital information in the memory 15. The control unit 12 thus functions as a vital information calculating section.

The vital information may be any information as long as it can be calculated based on a pulse wave. The control unit 12 calculates, as the vital information, for example, blood pressure information such as an SBP (systolic blood pressure) and a DBP (diastolic blood pressure), pulse information such as a pulse count, or heart rate information such as a heart rate.

Incidentally, the vital information calculating section may be included in another electronic equipment different from the vital information measuring device. In this case, the pressure signals stored in the memory 15 of the vital information measuring device are transmitted to the electronic equipment, and vital information is calculated and stored in the electronic equipment.

The control unit 12 determines the first value among a plurality of values of the pitch angle based on the pressure signals detected by the pressure detecting elements of the sensor section 6 during increase of a pressing force applied to the sensor section 6 against the body surface by the air bag 2, controls the pitch angle to the thus determined first value using the rotation drive section 10, and in a state where the pressing force is further increased from the thus controlled state, determines the second value from a plurality of roll angles based on DC components of the pressure signals detected by the pressure detecting elements of the sensor section 6. The control unit 12 thus functions as a rotation angle determining section.

The pulse wave detection unit 100, the rotation drive section 10, the air bag drive section 11 and functional blocks of the control unit 12 (the pressing force control section, the rotation control section, the reference level setting section, the storage control section and the rotation angle determining section) together construct a pulse wave detecting device.

Now, an operation of the vital information measuring device of the present embodiment will be described. The vital information measuring device of the present embodiment has a continuous blood pressure measurement mode in which the SBP and the DBP are calculated every heart rate to be displayed in the display section 13.

FIG. 6 is a flowchart used for explaining an operation in the continuous blood measurement mode of the vital information measuring device of the present embodiment.

Incidentally, in an initial state before a blood pressure measurement instruction is issued, it is assumed that the pitch angle and the roll angle are both set to, for example, 0 (zero) degree, and the pressing surface 6 b is vertical to the pressing direction in the pulse wave detection unit 100.

Here, the state where the pitch angle and the roll angle are respectively set to 0 (zero) degree is defined as the initial state, which does not limit the present invention. For example, a state where the rotation drive section 10 roll-rotates or pitch-rotates the sensor section 6 so that, with the pulse wave detection unit 100 worn on the wrist, the pressing surface 6 b can be placed in uniform contact with the skin in accordance with the shape of the wrist may be defined as the initial state.

When a blood pressure measurement instruction is issued, the control unit 12 obtains the temperature information detected by the temperature detecting section 7, and sets, based on the temperature information, the reference level of the pressure signal detected by each of the pressure detecting elements 6 a and 7 a of the sensor section 6 (step S1).

In the present embodiment, as each of the pressure detecting elements 6 a and 7 a included in the sensor section 6, an element in which a pressure signal (an offset level) detected with the pressing surface 6 b in contact with nothing is varied depending on the temperature, is used.

Therefore, based on the temperature detected by the temperature detecting section 7, the control unit 12 sets the reference level of the pressure signals detected by the pressure detecting elements 6 a and 7 a. Owing to the setting of the reference level, the levels of the pressure signals detected by the pressure detecting elements 6 a and 7 a are processed as values based on the set reference level.

Each of the pressure signals detected by the pressure detecting elements 6 a and 7 a includes a DC component independent of the heart rate and an AC component varied in accordance with the heart rate. A level of a rising point in a waveform of the pressure signal varied in accordance with the heart rate corresponds to the level of the DC component (the DC level). A difference between the rising point in the waveform of the pressure signal varied in accordance with the heart rate and a peak corresponds to the level of the AC component (the AC level).

After step S1, the control unit 12 controls the air bag drive section 11 to start injecting air into the air bag 2, so as to increase the pressing force applied by the sensor section 6 to the body surface (step S2).

The control unit 12 performs the control of the pitch angle based on the pressure signals detected by the pressure detecting elements of each of the element row 60 and the element row 70 during the increase of the pressing force started in step S2, and the selection of either of the element row 60 and the element row 70 (step S3).

Here, the control unit 12 selects, from the element row 60 and the element row 70, the element row that has been able to more rapidly occlude the radial artery T during the increase. Now, the processing performed in step S3 will be described in detail with reference to FIG. 7.

FIG. 7 is a flowchart used for explaining details of step S3 of FIG. 6.

During the increase of the pressing force started in step S2, the control unit 12 determines, based on the pressure signal detected by each of the pressure detecting elements 6 a of the element row 60, a target element (hereinafter referred to as the first target element) corresponding to one pressure detecting element positioned above the radial artery T out of all the pressure detecting elements 6 a included in the element row 60 (step S30).

For example, the control unit 12 divides the pressure signal detected by each pressure detecting element 6 a into the AC component and the DC component at arbitrary timing, and determines, as the first target element, a pressure detecting element 6 a having an AC level equal to or more than an AC threshold value and having a DC level equal to or less than a DC threshold value.

Besides, when there are a plurality of pressure detecting elements 6 a having an AC level equal to or more than the AC threshold value and having a DC level equal to or less than the DC threshold value, the control unit 12 determines, as the first target element, one having the maximum AC level and the minimum DC level out of the plural pressure detecting elements 6 a.

The control unit 12 stores, in the RAM, an ID of the element row 60, an ID of the first target element determined in step S30, a pressure signal detected by the first target element, detection time of the pressure signal, and a pressing force applied by the air bag 2 at the detection time in association with one another (step S31).

Concurrently with the processing of step S30 and step S31, the control unit 12 performs processing of step S32 and step S33.

In step S32, the control unit 12 determines a target element corresponding to one pressure detecting element position above the radial artery T (hereinafter referred to as the second target element) from all the pressure detecting elements 7 a included in the element row 70 based on the pressure signals detected by the pressure detecting elements 7 a of the element row 70 during the increase of the pressing force started in step S2.

A method for determining the second target element is the same as the method for determining the first target element. It is noted that the processing of step S32 is performed at the same time as the processing of step S30.

In step S33 following step S32, the control unit 12 stores, in the RAM, an ID of the element row 70, an ID of the second target element determined in step S32, the pressure signal detected by the second target element, the detection time of the pressure signal and the pressing force applied by the air bag 2 at the detection time in association with one another.

After step S31 and step S33, the control unit 12 determines, based on the pressure signals at the respective detection times stored in the RAM, whether or not each of an AC level of the pressure signal detected by the first target element determined in step S30 and an AC level of the pressure signal detected by the second target element determined in step S32 has passed a peak (step S34).

Specifically, the control unit 12 compares a first AC level of a pressure signal corresponding to detection time immediately before the detection time of the pressure signal of the first target element determined in step S30 with a second AC level of the pressure signal of the first target element determined in step S30.

Then, when the second AC level is lower than the first AC level by a value equal to or more than a threshold value, the control unit 12 determines that the AC level of the pressure signal detected by the first target element determined in step S30 has passed the peak.

When the second AC level is not lower than the first AC level by the value equal to or more than the threshold value, or when merely one AC level of the pressure signal of the first target element is stored in the RAM, the control unit 12 determines that the AC level of the pressure signal detected by the first target element determined in step S30 has not passed the peak.

Similarly, the control unit 12 compares a third AC level of a pressure signal corresponding to detection time immediately before the detection time of the pressure signal of the second target element determined in step S32 with a fourth AC level of the pressure signal of the second target element determined in step S32.

Then, when the fourth AC level is lower than the third AC level by a value equal to or more than a threshold value, the control unit 12 determines that the AC level of the pressure signal detected by the second target element determined in step S32 has passed the peak.

When the fourth AC level is not lower than the third AC level by the value equal to or more than the threshold value, or when merely one AC level of the pressure signal of the second target element is stored in the RAM, the control unit 12 determines that the AC level of the pressure signal detected by the second target element determined in step S32 has not passed the peak.

When it is determined as NO in step S34, the control unit 12 calculates a difference (an AC level difference) between the AC level of the pressure signal detected by the first target element determined in step S30 and the AC level of the pressure signal detected by the second target element determined in step S32, and determines whether or not the calculated AC level difference is equal to or more than a rotation threshold value (step S35).

When the AC level difference is equal to or more than the rotation threshold value (step S35: YES), the control unit 12 determines that the element row including the target element having a relatively low AC level cannot satisfactorily flatten the radial artery T, and determines that pitch rotation is necessary. Then, the control unit 12 pitch-rotates the sensor section 6 in a direction where this element row comes closer to the body surface (step S36).

For example, when the latest AC level of the first target element at the time of the determination in step S35 is higher than the latest AC level of the pressure signal of the second element at the same time point by a value equal to or more than the rotation threshold value, the control unit 12 pitch-rotates the sensor section 6 in the negative direction. Thus, the AC levels of the pressure signals detected by the first target element and the second target element can be made close to each other.

The control unit 12 returns the processing to step S30 and step S32 after the processing of step S36.

A rotation amount in pitch-rotating the sensor section 6 in step S36 may be, for example, a controllable minimum value, or may be a value precedently determined in accordance with the AC level difference calculated in step S35. When the rotation amount is a value in accordance with the AC level difference, for example, the control unit 12 increases the rotation amount as the AC level difference is larger.

Incidentally, when the processing of step S36 has been performed, the AC levels of the pressure signals respectively detected by the first target element and the second target element are largely varied as compared with those before performing the processing. Therefore, in the processing of step S34 performed immediately after performing the processing of step S36, it is determined whether or not the AC level has passed the peak in consideration of this variation of the AC level.

For example, the control unit 12 forcedly determines as NO in step S34 performed after the processing of step S36 to perform the processing of step S35.

When the AC level difference is smaller than the rotation threshold value (step S35: NO), the control unit 12 determines that the two element rows respectively satisfactorily flatten the radial artery T, determines that there is no need of the pitch rotation, and returns the processing to step S30 and step S32.

When it is determined as YES in step S34, the control unit 12 determines whether or not the AC level of the pressure signal detected by the first target element has reached an occlusion completion determination threshold value (a first threshold value) smaller than a maximum value of the AC levels of the pressure signals corresponding to the element row 60 stored in the RAM, or whether or not the AC level of the pressure signal detected by the second target element has reached an occlusion completion determination threshold value (a second threshold value) smaller than a maximum value of the AC levels of the pressure signals corresponding to the element row 70 stored in the RAM (step S37).

Incidentally, at the time when it is determined as YES in step S34, the pitch angle of the sensor section 6 employed at this time point is determined as an optimal pitch angle to be employed by control in the processing of step S11 and following steps. In other words, in a period from the start of the increase of the pressing force in step S2 until the AC level of the pressure signal detected by each of the first target element and the second target element reaches the maximum value, the optimal pitch angle is determined.

The first threshold value is set to a value obtained by multiplying the maximum value of the AC levels of the pressure signals detected by the first target elements stored in the RAM by a coefficient α larger than 0 (zero) and smaller than 1. The second threshold value is set to a value obtained by multiplying the maximum value of the AC levels of the pressure signals detected by the second target elements stored in the RAM by the coefficient α.

The occlusion completion determination threshold value is a value used for determining whether or not the radial artery T has been occluded by the element row 60 or the element row 70. The coefficient α is set to a value sufficient for assuring determination accuracy for this purpose. The coefficient α is set to, for example, 0.5.

When it is determined as NO in step S37, the control unit 12 returns the processing to step S30 and step S32.

When it is determined as YES in step S37, namely, when the AC level of the pressure signal detected by the first target element has reached the first threshold value, or when the AC level of the pressure signal detected by the second target element has reached the second threshold value, the control unit 12 selects, from the element row 60 and the element row 70, an element row including a target element whose AC level has priorly reached the occlusion completion determination threshold value (step S38).

The control unit 12 halts the processing of step S30 to step S33 when the element row is selected in step S38. The element row selected in step S38 will be hereinafter referred to as the selected element row.

Next, the control unit 12 sets, as a first pressing value, a pressing force (HDP_(max)) of the air bag 2 applied at the time when the AC level of the target element determined in the above-described selected element row stored in the RAM has reached the occlusion completion determination threshold value (step S39). Among the target elements determined in the selected element row, a target element determined when its AC level has reached the occlusion completion determination threshold value is sometimes referred to as the target element at the time of the occlusion completion.

Next, the control unit 12 sets, as a second pressing value, a pressing force (HDP_(ACmax)) of the air bag 2 applied at the time when the AC level of the target element determined in the above-described selected element row stored in the RAM has reached the maximum value (step S40).

Here, one of the element row 60 and the element row 70 is selected as the selected element row based on the pressure signals detected by the pressure detecting elements 6 a and 7 a, but it may be precedently determined which of the element row 60 and the element row 70 included in the sensor section 6 is to be selected as the selected row element.

For example, when the element row 60 is precedently set as the selected element row, the element 60 is selected as the selected element row in step S38. Besides, it is determined in step S34 whether or not the AC level of the first target element has passed the peak, and it is determined in step S37 whether or not the AC level of the first target element has reached the occlusion completion determination threshold value.

FIG. 8 is a diagram illustrating change in the pressure signal detected by the target element determined in the selected element row selected in step S38 of FIG. 7. The abscissa indicates time and the ordinate indicates a pressure value. A pressure value at each time corresponds to the level of the pressure signal detected by the target element determined at that time.

When a blood pressure measurement instruction is issued, the reference level of the sensor section 6 is set before time t0 (step S1 of FIG. 6). Then, the pressing force increase is started at time t0 (step S2 of FIG. 6).

When the pressing force starts to increase, the AC level of the pressure signal detected by the target element reaches the peak (AC_(max)) at time t1, and reaches a value obtained by multiplying AC_(max) by the coefficient α (0.5 here) at time t2. Then, the selected element row is determined at time t2 (step S38 of FIG. 7).

Besides, in a period between time t0 and time t1, it is determined, based on the AC level of the pressure signal detected by the first target element and the AC level of the pressure signal detected by the second target element, whether or not the pitch rotation is necessary, and when the pitch rotation is necessary, the pitch rotation is performed (step S36 of FIG. 7).

Incidentally, in a period between time t0 and time t2, the target element positioned above the radial artery T is determined at at each time in each of the element rows 60 and 70 as illustrated in FIG. 7.

At time t2, the pressing force (HDP_(max)) applied at time t2 is set as the first pressing value (step S39 of FIG. 7). Besides, at time t2, the pressing force (HDP_(ACmax)) applied at time t1 is set as the second pressing value (step S40 of FIG. 7).

Referring to FIG. 6 again, when the optimal pitch angle and the selected element row are determined by the processing of step S3, the control unit 12 controls the pressing force applied by the air bag 2 to the first pressing value set in step S39 of FIG. 7, and holds the pressing force in this state (step S4).

In a state where the pressing force is held at the first pressing value, the control unit 12 obtains DC levels detected by the plural pressure detecting elements included in the selected element row, and determines, based on the obtained DC levels, a roll angle (hereinafter referred to as the optimal roll angle) to be employed by control at the time of generating correction data in step S11 and following steps, and at the time of continuous blood pressure measurement (step S5).

FIG. 9 is a flowchart used for explaining details of step S5 of FIG. 6.

First, the control unit 12 controls the rotation drive section 10 to control the roll angle to an arbitrary value (step S51).

Next, the control unit 12 obtains the DC levels of pressure signals respectively detected by a first pressure detecting element (a target element determined at time t2 of FIG. 8) corresponding to the target element at the time of the occlusion completion among the pressure detecting elements of the selected element row, a second pressure detecting element adjacent on the radius side to the first pressure detecting element, and a third pressure detecting element adjacent on the ulna side to the first pressure detecting element (step S52).

Next, the control unit 12 calculates flatness of a graph corresponding to the relationship among the obtained three DC levels and the positions of the first to the third pressure detecting elements, and stores, in the RAM, the calculated flatness in association with the value of the roll angle currently employed by control (step S53).

For example, the control unit 12 obtains dispersion or standard deviation of the three DC levels, and regards the reciprocal of the obtained dispersion or standard deviation as the flatness. The flatness is defined as a numerical value corresponding to smallness of variation of these three DC levels.

Next, the control unit 12 determines whether or not the flatness has been calculated with respect to each of all the controllable roll angles (step S54).

When the flatness has not been calculated with respect to all the controllable roll angles (step S54: NO), the control unit 12 controls the rotation drive section 10 to make a change to a roll angle for which the flatness has not been calculated (step S55), and thereafter, the processing of step S52 and following steps is performed.

When the flatness has been calculated with respect to all the roll angles (step S54: YES), the control unit 12 determines, as the optimal roll angle, a roll angle in association with the maximum flatness (namely, the minimum variation of the DC levels) among the roll angles stored in the RAM through the processing of step S53 (step S56). Incidentally, it is preferable that the control unit 12 waits for a prescribed time period after controlling the roll angle to an arbitrary value in step S51, and obtains the DC levels of the pressure signals detected by the first to third pressure detecting elements of the selected element row at timing after the time period has elapsed. Immediately after changing the roll angle from one value to another value, a pressing posture of the sensor section 6 against the body surface is changed, and hence, there is a possibility that the blood flow is largely varied. Therefore, when the DC levels of the pressure signals are detected after waiting for a little after the control of the roll angle to an arbitrary value, the influence of such blood flow variation can be reduced.

FIGS. 10A to 10C are diagrams illustrating states where the roll angle of the pulse wave detection unit 100 of FIG. 1 is controlled to three values. FIG. 10A illustrates a state where the roll angle is controlled to +θa degrees. FIG. 10B illustrates a state where the roll angle is controlled to 0 (zero) degree. FIG. 10C illustrates a state where the roll angle is controlled to −θa degrees. It is noted that θa is an arbitrary value.

FIG. 11 is a graph illustrating a relationship between a DC level of a pressure signal detected by each pressure detecting element of the selected element row with the roll angle controlled as illustrated in FIGS. 10A to 10C and the position of the pressure detecting element.

A curve 110 illustrated in FIG. 11 corresponds to an example of the DC level of the pressure signal detected by each pressure detecting element in the state of FIG. 10A. In the state of FIG. 10A, the end of the selected element row on the side of the radius TB is in a position close to the radius TB. Therefore, the curve 110 has a shape having a higher DC level in the end on the side of the radius TB.

A curve 111 illustrated in FIG. 11 corresponds to an example of the DC level of the pressure signal detected by each pressure detecting element in the state of FIG. 10B. In the state of FIG. 10B, a pressure from the radius TB is lower than in the state of FIG. 10A. Therefore, the inclination of the curve 111 is gentle as compared with the inclination of the curve 110.

A curve 112 illustrated in FIG. 11 corresponds to an example of the DC level of the pressure signal detected by each pressure detecting element in the state of FIG. 10C. In the state of FIG. 10C, the pressure from the radius TB is lower than in the state of FIG. 10B. Therefore, the inclination of the curve 112 is gentle as compared with the inclination of the curve 111, and has the highest flatness among the three curves 110, 111 and 112.

In this manner, when the DC level of the pressure signal detected by each pressure detecting element of the element row is observed, a distribution of the pressure from a hard tissue such as a bone or a tendon can be grasped.

Incidentally, the pressing force employed in determining the optimal roll angle preferably has a value that is not too large to cause a change in the curve such as the curves 110 to 112 by changing the roll angle. Besides, the pressing force employed in determining the optimal roll angle preferably has a value that is sufficiently large for detecting a pressure signal from a hard tissue (for sufficiently occluding the radial artery T).

In other words, when the coefficient α is set to an appropriate value, the pressing force employed in determining the optimal roll angle can be set to an appropriate magnitude, and hence, a distribution of the pressure from a hard tissue can be accurately grasped.

Each curve illustrated in FIG. 11 is formed by using DC levels of pressure signals detected by all the pressure detecting elements included in the selected element row. Below the selected element row, the radius, the radial artery and the tendon are present in this order. Therefore, the shape of each curve illustrated in FIG. 11 can be mainly any of the following three patterns: A shape in which a pressure from the radius is strongly detected, and a DC level of a pressure detecting element, which is positioned closest to the radius (in the radius-side end) out of the pressure detecting elements included in the selected element row, is higher than a DC level of a pressure detecting element, which is positioned closest to the ulna (in the ulna-side end); a shape in which a pressure from a tendon is strongly detected, and the DC level of the pressure detecting element in the radius-side end is lower than the DC level of the pressure detecting element in the ulna-side end; and a flat shape.

Accordingly, in step S53 of FIG. 9, the control unit 12 may calculate the flatness of each curve illustrated in FIG. 11 with the pressure detecting element in the radius-side end among the pressure detecting elements included in the selected element row regarded as the second pressure detecting element, and with the pressure detecting element in the ulna-side end among the pressure detecting elements included in the selected element row regarded as the third pressure detecting element.

Alternatively, the control unit 12 may obtain, in step S52 of FIG. 9, the DC levels of the pressure signals detected by the two pressure detecting elements respectively positioned in the radius-side end and the ulna-side end of the selected element row, and may define, in step S53 of FIG. 9, a reciprocal of a difference between these two DC levels as the flatness of the curve illustrated in FIG. 11.

When a graph illustrating the relationship between the positions of the plural pressure detecting elements included in the selected element row and the DC levels detected by these is flatter, it means that the influence of the pressure from a hard tissue is smaller and the radial artery T can be pressed without being disturbed by the hard tissue.

In order to obtain a state where the radial artery T can be pressed without being disturbed by a hard tissue, the control unit 12 calculates the flatness with respect to each of all the controllable roll angles, and determines, as the optimal roll angle, a roll angle whose flatness thus calculated has the maximum value.

Incidentally, the control unit 12 may calculate the flatness based on variation in the DC level of pressure signals detected by all the pressure detecting elements included in the selected element row, so as to determine, as the optimal roll angle, a roll angle whose flatness thus calculated has the maximum value.

As described above, when the number of DC levels used for the calculation of the flatness is limited to two or three, computational complexity can be reduced. As a result, reduction of power consumption and fast determination of the optimal roll angle can be realized.

Besides, the control unit 12 determines the optimal roll angle based on the DC levels of the pressure signals detected by a plurality of pressure detecting elements of one element row selected from the element row 60 and the element row 70 in step S5 of FIG. 6, which does not limit the present invention. The control unit 12 may determine the optimal roll angle based on DC levels of pressure signals detected by the pressure detecting elements of each of the element row 60 and the element row 70.

For example, the control unit 12 obtains DC levels of the pressure signals detected by the plural pressure detecting elements in each of the element row 60 and the element row 70 in step S52 of FIG. 9.

Then, in step S53 of FIG. 9, the control unit 12 calculates the flatness based on the plural DC levels obtained with respect to the element row 60, stores the result in association with a roll angle currently employed by control, calculates the flatness based on the plural DC levels obtained with respect to the element row 70, and stores the result in association with the roll angle currently employed by control.

After calculating the flatness of each element row with respect to all the roll angles, the control unit 12 may determine the roll angle in association with the maximum flatness as the optimal roll angle in step S56 of FIG. 9.

Referring to FIG. 6 again, after step S5, the control unit 12 controls the roll angle of the sensor section 6 to the optimal roll angle determined in step S5 (step S6).

The processing of step S5 to step S6 will be described with reference to FIG. 8. Incidentally, FIG. 8 illustrates exemplified operations performed when the roll angle can be controlled to the three values of 0 (zero) degree, +θ1 degrees and −θ1 degrees. It is noted that θ1 is an arbitrary value.

As illustrated in FIG. 8, the roll angle is controlled to 0 (zero) degree in a period from time t2 to time t3, and the flatness is calculated in this state. Subsequently, in a period from time t3 to time t4, the roll angle is controlled to +θ1 degrees, and the flatness is calculated in this state. Subsequently, in a period from time t4 to time t5, the roll angle is controlled to −θ1 degrees, and the flatness is calculated in this state.

In the exemplified case illustrated in FIG. 8, the flatness calculated in the state where the roll angle is controlled to 0 (zero) degree is the maximum (the optimal roll angle=0 (zero) degree). Therefore, the control unit 12 controls the roll angle of the sensor section 6 to 0 (zero) degree in a period from time t5 to time t6. Besides, the control unit 12 holds the pressing force at the second pressing value (HDP_(ACmax)) in the period from time t5 to time t6.

Incidentally, since the roll angle corresponding to the maximum flatness is 0 (zero) degree in the exemplified case of FIG. 8, the roll angle is changed from −θ1 degrees to 0 (zero) degree in the period from time t5 to time t6. If the flatness is maximum in the period from time t4 to time t5, however, there is no need to change the roll angle in the period from time t5 to time t6. In other words, the determination of the optimal roll angle and the control to the optimal roll angle may be simultaneously performed.

Referring to FIG. 6 again, the control unit 12 reduces the pressing force applied by the air bag 2 to a reset value (a value HDP_(RESET) illustrated in FIG. 8) smaller than the second pressing value set in step S40 and larger than 0 (zero), and holds the pressing force at this reset value (step S7, time t7 of FIG. 8).

The control unit 12 obtains, in this state, the temperature information detected by the temperature detecting section 7, calculates a difference between the obtained temperature information and the temperature information obtained in step S1, and determines whether or not the difference is equal to or more than a temperature threshold value (step S8).

When it is determined that the difference is less than the temperature threshold value, namely, it is determined that there is no large difference in the temperature of the sensor section 6 between the time of the processing of step S1 and the current time (step S8: NO), the control unit 12 performs processing of step S11.

When it is determined that the difference is equal to or more than the temperature threshold value, namely, it is determined that there is a large difference in the temperature of the sensor section 6 between the time of the processing of step S1 and the current time (step S8: YES), the control unit 12 controls the pressing force to 0 (zero) (step S9), and thereafter, re-sets the reference level of the pressure signal detected by each pressure detecting element of the sensor section 6 based on the current temperature information (step S10). After step S10, the processing of step S11 and following steps is started.

In step S11, the control unit 12 increases the pressing force from the current value to a precedently determined value sufficient for occluding the radial artery T (from time t7 to time t8 of FIG. 8).

The control unit 12 controls a rate of increasing the pressing force in step S11 to a lower rate than a rate of increasing the pressing force in step S2, which does not limit the invention.

Incidentally, the processing of step S8 to step S10 of FIG. 6 is not indispensable but can be omitted. In this case, the processing of step S11 follows step S7.

The control unit 12 stores, in the memory 15, the pressure signals detected by the pressure detecting elements of the sensor section 6 during the increase of the pressing force started in step S11, and based on the pressure signals thus stored, determines an optimal pressure detecting element out of all the pressure detecting elements 6 a and 7 a.

The control unit 12 determines, for example, a pressure detecting element having detected a pressure signal having the maximum AC level during the increase of the pressing force as the optimal pressure detecting element. Besides, the control unit 12 determines, as an optimal pressing force, a pressing force applied when this pressure signal is detected (step S12).

After step S12, the control unit 12 generates pulse wave envelope data based on the pressure signals detected by the optimal pressure detecting element during the increase of the pressing force and stored in the memory 15.

The pulse wave envelope data is data in which the pressing force of the sensor section 6 (the internal pressure of the air bag 2) is in association with the AC level of the pressure signal detected by the optimal pressure detecting element in a state where the optimal pressure detecting element is pressed against the body surface with that pressing force.

Then, the control unit 12 calculates the SBP and the DBP based on the thus generated pulse wave envelope data, and generates the correction data to be used in continuous blood pressure measurement of step S15 based on the pressure signals detected by the optimal pressure detecting element during the increase of the pressing force started in step S11 and the calculated SBP and DBP, and stores the correction data in the memory 15 (step S13).

Thereafter, the control unit 12 holds the pressing force at the optimal pressing force determined in step S12 (step S14, time t9 of FIG. 8).

Then, the control unit 12 successively stores, in the memory 15, the pressure signals detected by the optimal pressure detecting element determined in step S12, and based on the AC levels of the pressure signals thus stored and the correction data generated in step S13, calculates the SBP and the DBP every heart rate and stores these in the memory 15 (step S15). The control unit 12 displays the calculated SBP and DBP in, for example, the display section 13 to inform the user.

The control unit 12 repeatedly performs the processing of step S15 until an instruction to stop the blood pressure measurement is issued, and when the stop instruction is issued, the blood pressure measurement processing is ended.

In this manner, in the vital information measuring device of the present embodiment, one of the element row 60 and the element row 70 is selected as the selected element row in step S3. Then, based on the pressure signals detected by the plural pressure detecting elements of the one selected element row, the optimal roll angle is determined.

Specifically, in step S3, the control unit 12 selects, as the selected element row, an element row having priorly occluded the radial artery T (an element row having the shortest elapsed time from the start of the increase of the pressing force in step S2 until the AC level of the pressure signal detected by the target element reaches the occlusion completion determination threshold value), and determines the optimal roll angle in a state where the pressing force applied at the time when the selected element row occluded the radial artery T is held.

Owing to this configuration, the optimal roll angle can be determined based on the pressure signals output from an element row not affected by blood flow change or the like caused by the occlusion of the radial artery T. In other words, the pressure signal output from the selected element row can be improved in the reliability, and the determination accuracy of the optimal roll angle can be improved.

Besides, since the element row that has been able to occlude the radial artery T in a shorter period of time is selected as the selected element row, time necessary for the determination of the optimal roll angle can be reduced to reduce time required for starting the blood pressure measurement.

Furthermore, in the vital information measuring device of the present embodiment, the optimal roll angle is determined based on the DC levels of the pressure signals detected by the pressure detecting elements of either one of the element rows 60 and 70. Since the optimal roll angle is thus determined based on the DC levels of the pressure signals, the roll angle minimally affected by a pressure from a hard tissue such as a bone or a tendon can be highly accurately determined.

Besides, in the vital information measuring device of the present embodiment, the optimal roll angle is determined in a state where the pressing force is controlled to the first pressing value. When the DC level of the pressure signal detected by the selected element in the state where the pressing force is controlled to the first pressing value is obtained in this manner, a distribution of the pressure from a hard tissue such as a bone or a tendon can be satisfactorily detected, and hence the determination accuracy of the optimal roll angle can be improved.

Incidentally, the control unit 12 may determine, in step S5 of FIG. 6, the optimal roll angle based on the absolute values of the pressure signals detected by the pressure detecting elements of the selected element row instead of the DC levels of the pressure signals detected by the pressure detecting elements of the selected element row.

The state where the pressing force is held at the first pressing value in step S4 of FIG. 6 is a state where the radial artery T is occluded by the selected element row. In other words, in this state, the AC levels of the pressure signals detected by the pressure detecting elements of the selected element row are sufficiently low.

Therefore, even when the optimal roll angle is determined based on the absolute values of the pressure signals detected by the plural pressure detecting elements of the selected element row, the influence of the pressure from a hard tissue such as a bone or a tendon can be reduced with given accuracy. When the DC levels are used as described above, a distribution of the pressure from a hard tissue such as a bone or a tendon can be more accurately detected, and hence the determination accuracy of the optimal roll angle can be improved.

Besides, in the vital information measuring device of the present embodiment, in a time period from the start of the increase of the pressing force in step S2 until the pressing force reaches the first pressing value, the pitch angle is controlled to the optimal pitch angle based on the AC levels of the pressure signals detected by the target elements determined in each of the element rows 60 and 70. Then, in a state where the pitch angle is controlled to the optimal pitch angle, the optimal roll angle is determined in step S5.

Since the optimal roll angle is thus determined in the state where the pitch angle is controlled to the optimal pitch angle, probabilities that the element row 60 and the element row 70 can be respectively determined as the selected element row in step S38 can be substantially the same. In other words, choices of the element rows usable for the determination of the optimal roll angle can be increased, and hence, the determination accuracy of the optimal roll angle can be improved.

At the time of obtaining a pressure signal necessary for generating the correction data and at the time of the continuous blood pressure measurement, in order to increase the pulse wave detection accuracy, an ideal pressing state where the pressing state of the radial artery T by the element row 60 is substantially equivalent to the pressing state of the radial artery T by the element row 70 is preferably obtained.

In the vital information measuring device of the present embodiment, since the pitch angle is controlled to the optimal pitch angle in the processing of step S3, the processing of step S11 and following steps can be performed in the ideal pressing state, and hence the pulse wave detection accuracy can be improved.

In the vital information measuring device of the present embodiment, the optimal pitch angle can be determined during the increase of the pressing force necessary for determining the optimal roll angle. Therefore, the determination of the optimal pitch angle and the optimal roll angle can be rapidly performed, and the time required for starting the blood pressure measurement can be reduced.

In the vital information measuring device of the present embodiment, the control unit 12 may determine the optimal pitch angle in step S3 based on the DC levels of the pressure signals detected by the plural pressure detecting elements included in each of the element rows 60 and 70.

Specifically, in step S35 of FIG. 7, the control unit 12 calculates a difference (a DC level difference) between the DC level of the pressure signal detected by the first target element and the DC level of the pressure signal detected by the second target element, and determines whether or not the calculated DC level difference is equal to or larger than a rotation threshold value.

When the DC level difference is equal to or larger than the rotation threshold value, the control unit 12 pitch-rotates the sensor section 6 by a rotation amount corresponding to the magnitude of the DC level difference or by a precedently determined rotation amount in step S36. When the DC level difference is smaller than the rotation threshold value, the control unit 12 returns the processing to step S30 and step S32.

Since the optimal pitch angle is thus determined based on the DC levels of the pressure signals, the optimal pitch angle with which the ideal pressing state can be realized can be highly accurately determined. The reason is as follows.

In the vital information measuring device of the present embodiment, the element row 60 and the element row 70 press different portions of a living body. Besides, when the radial artery T is started to be occluded on the peripheral side having high resistance prior to the center side, a reflected wave is caused accordingly. The reflected wave is superimposed on a pressure signal detected by a pressure detecting element of the element row 70 positioned above the radial artery T.

In this manner, due to a difference in the composition of a subcutaneous tissue of the pressed portion of the living body, and the occurrence of a reflected wave and the like, even in the ideal pressing state, the AC level of a pressure signal detected by a pressure detecting element of the element 60 positioned above the radial artery T may be different from the AC level of a pressure signal detected by a pressure detecting element of the element row 70 positioned above the radial artery T in some cases.

On the other hand, the DC level of the pressure signal detected by the pressure detecting element of the element row 60 positioned above the radial artery T and the DC level of the pressure signal detected by the pressure detecting element of the element row 70 positioned above the radial artery T are not affected by the difference in the composition of the subcutaneous tissue of the pressed portion of the living body, and the occurrence of a reflected wave and the like.

Therefore, when the optimal pitch angle is determined based on the DC levels of the pressure signals detected by the plural pressure detecting elements included in each of the element rows 60 and 70, the optimal pitch angle can be highly accurately determined.

Incidentally, also when the optimal pitch angle is determined based on the AC levels of the pressure signals detected by the plural pressure detecting elements included in each of the element rows 60 and 70, the optimal pitch angle can be determined with given accuracy.

Furthermore, in the vital information measuring device of the present embodiment, the optimal pitch angle can be determined based on pressure signals respectively detected by two pressure detecting elements, that is, one pressure detecting element selected from the element row 60 and one pressure detecting element selected from the element row 70.

When the optimal pitch angle is thus determined based on the pressure signals of the two pressure detecting elements, the computational complexity necessary for determining the optimal pitch angle can be reduced, so as to reduce the power consumption and reduce the time required for starting the blood pressure measurement.

Besides, in the vital information measuring device of the present embodiment, after determining the optimal pitch angle, the pressing force is reduced to the reset value smaller than the second pressing value and larger than 0 (zero), and thereafter, the processing of step S11 and following steps is performed. When the processing of step S11 and following steps is thus performed without reducing the pressing force to 0 (zero), the time required for starting the blood pressure measurement can be reduced.

Furthermore, when the processing of step S11 and following steps is performed with the pressing force once reduced, the optimal pressing force and the optimal pressure detecting element can be determined with the sensor section 6 controlled to the optimal roll angle and the optimal pitch angle, and hence the pulse wave detection accuracy can be improved.

Besides, the vital information measuring device of the present embodiment re-sets, after determining the optimal pitch angle and the optimal roll angle, the reference level of each pressure detecting element of the sensor section 6 with the pressing force reduced to 0 (zero) when there has arisen a large difference between the temperature information obtained at the initial state and the current temperature information. When the reference revel is thus re-set, the pulse wave detection accuracy in the processing of step S11 and following steps can be improved.

Furthermore, in the vital information measuring device of the present embodiment, the rate of increasing the pressing force in step S2 is higher than the rate of increasing the pressing force in step S11.

Owing to this configuration, the increase of the pressing force necessary for determining the optimal roll angle and the optimal pitch angle can be rapidly performed, and the time required for starting the blood pressure measurement can be reduced. On the other hand, since the rate of increasing the pressing force necessary for generating the correction data is relatively low, the correction data can be highly accurately obtained.

FIG. 12 is a flowchart illustrating a modification of the detailed processing of step S5 of FIG. 6.

First, the control unit 12 controls the rotation drive section 10 to control the roll angle to an arbitrary angle (step S91).

Next, the control unit 12 obtains the DC levels of pressure signals respectively detected by the first pressure detecting element to the third pressure detecting element among the respective pressure detecting elements of the selected element row, calculates the flatness in the same manner as in the processing of step S53 based on the three DC levels thus obtained, and stores the flatness in the RAM in association with the roll angle currently employed by control (step S92).

Next, the control unit 12 determines whether or not a difference between the DC level of the pressure signal detected by the second pressure detecting element (hereinafter referred to as the radius-side DC level) and the DC level of the pressure signal detected by the third pressure detecting element (hereinafter referred to as the ulna-side DC level) is equal to or more than a threshold value (step S93).

When the difference between the radius-side DC level and the ulna-side DC level is less than the threshold value (step S93: NO), the control unit 12 controls the rotation drive section 10 to roll-rotate the sensor section 6 by a minimum angle in the positive direction or the negative direction (step S94), and thereafter, returns the processing to step S92.

When the difference between the radius-side DC level and the ulna-side DC level is equal to or more than the threshold value (step S93: YES), the control unit 12 determines whether or not the radius-aide DC level is higher than the ulna-side DC level (step S95).

When the radius-side DC level is lower than the ulna-side DC level (step S95: NO), the control unit 12 restricts the direction of the roll rotation to the positive direction (the counterclockwise direction taken from the side of the left elbow) (step S96). In other words, the control unit 12 excludes, from candidates of the optimal roll angle, roll angles toward the negative direction from the current roll angle out of roll angles excluding roll angles having been calculated for the flatness.

When the radius-side DC level is higher than the ulna-side DC level (step S95: YES), the control unit 12 restricts the direction of the roll rotation to the negative direction (the clockwise direction taken from the side of the left elbow) (step S97). In other words, the control unit 12 excludes, from the candidates of the optimal roll angle, roll angles toward the positive direction from the current roll angle out of the roll angles excluding the roll angles having been calculated for the flatness.

After step S96 and step S97, the control unit 12 determines whether or not the flatness has been calculated for all angles in the rotation direction restricted based on the current roll angle as described above out of all the settable roll angles (step S98).

When it is determined as NO in step S98, the control unit 12 controls the rotation drive section 10 to control the sensor section 6 to a roll angle not calculated for the flatness yet among the settable roll angles in the restricted rotation direction (step S99).

Then, the control unit 12 obtains the DC levels of the pressure signals respectively detected by the first pressure detecting element to the third pressure detecting element, calculates the flatness in the same manner as in the processing of step S52 based on the obtained three DC levels, and stores the flatness in the RAM in association with the roll angle currently employed by control (step S100). After step S100, the processing returns to step S98.

When it is determined as YES in step S98, the control unit 12 determines, as the optimal roll angle, a roll angle in association with the largest flatness out of the roll angles stored in the RAM through the processing of step S92 and step S100 (step S1θ1).

In this manner, according to the modification illustrated in FIG. 12, as compared with the exemplified processing illustrated in FIG. 9, the number of roll angles to be calculated for the flatness can be reduced. Therefore, the computation complexity for determining the optimal roll angle can be reduced, and the power consumption caused in the roll rotation can be reduced.

Incidentally, it is assumed here that the angles settable as the roll angle are three angles of 0 (zero) degree, +θ1 degrees and −θ1 degrees (wherein θ1 is an arbitrary value), and that the arbitrary value used in step S91 is 0 (zero) degree.

In this case, when the processing of the initial step S93 is determined as YES and step S95 is determined as NO, the control unit 12 determines +θ1 degrees as the optimal roll angle. Alternatively, when the processing of the initial step S93 is determined as YES and step S95 is determined as YES, the control unit 12 determines −θ1 degrees as the optimal roll angle.

In this manner, according to this modification, the optimal roll angle can be also determined without performing the roll rotation.

It should be understood that the present embodiment herein disclosed is merely illustrative and not restrictive. The scope of the present invention is not limited to the above description but is defined by appended claims, and it is intended that equivalents to the appended claims and all changes made within the scope thereof are embraced.

For example, the wrist-worn vital information measuring device for detecting a pulse wave from the radial artery of a wrist has been described so far, but the present invention may be applied to a device for detecting a pulse wave from the carotid artery or the dorsalis pedis artery.

Besides, the sensor section 6 may be configured to include three or more element rows arranged in the direction A.

In the case of employing this configuration, the control unit 12 selects, in step S3 of FIG. 6, an element row having occluded the radial artery T most early among the three or more element rows as the selected element row. Alternatively, the control unit 12 precedently selects any one of the three or more element rows as the selected element row.

Besides, in step S3 of FIG. 6, the control unit 12 controls the pitch angle to the optimal pitch angle with which the DC levels or the AC levels of pressure signals detected by pressure detecting elements respectively selected from the three or more element rows are close to one another.

A pulse wave detecting device herein disclosed includes: a sensor section in which a plurality of element rows each including a plurality of pressure detecting elements arranged in a first direction are arranged in a direction perpendicular to the first direction; a pressing section that presses the sensor section against a body surface of a living body in a state where the first direction crosses a direction of extending an artery below the body surface; a rotation drive section that rotates the sensor section about each of two axes perpendicular to a pressing direction of the pressing section, the two axes being a first axis extending in the first direction and a second axis perpendicular to the first direction; a storage control section that stores, in a storage medium, pressure signals detected by the pressure detecting elements in a state where a first rotation angle of the sensor section about the first axis is controlled to a first value, a second rotation angle of the sensor section about the second axis is controlled to a second value, and the sensor section is pressed against the body surface by the pressing section; and a rotation angle determining section that determines the first value based on the pressure signals detected by the pressure detecting elements during increase of a pressing force applied to the sensor section against the body surface by the pressing section, controls the first rotation angle to the determined first value using the rotation drive section, and determines the second value based on DC components of the pressure signals detected by the pressure detecting elements in a state where the pressing force is further increased from the thus controlled state.

In the disclosed pulse wave detecting device, the rotation angle determining section determines the first value based on the pressure signals detected by the plurality of pressure detecting elements included in each of the plurality of element rows.

In the disclosed pulse wave detecting device, the rotation angle determining section determines the second value based on the DC components of the pressure signals detected by the plurality of pressure detecting elements included in a selected element row corresponding to one element row selected from the plurality of element rows.

In the disclosed pulse wave detecting device, the rotation angle determining section performs processing for successively determining, as a target element, during the increase, one element positioned above the artery out of the pressure detecting elements included in the element rows based on a pressure signal group detected by the pressure detecting elements of the element rows, and selects, as the selected element row among the plurality of element rows, an element row having shortest elapsed time from start of the increase to time when a signal level of an AC component of a pressure signal detected by the successively determined target element reaches, after reaching a maximum value, a threshold value specified with reference to the maximum value and smaller than the maximum value.

In the disclosed pulse wave detecting device, the rotation angle determining section determines the second value in a state where the sensor section is pressed against the body surface with the pressing force applied at the time when the signal level of the AC component of the pressure signal detected by the target element of the selected element row reaches the threshold value.

In the disclosed pulse wave detecting device, the rotation angle determining section performs processing for successively determining, as a target element, during the increase of the pressing force, one element positioned above the artery out of the pressure detecting elements included in the selected element row based on a pressure signal group detected by the pressure detecting elements of the selected element row, and determines the second value in a state where the sensor section is pressed against the body surface with a pressing force larger than the pressing force applied at the time when a signal level of an AC component of a pressure signal detected by the successively determined target element reaches a maximum value.

In the disclosed pulse wave detecting device, the rotation angle determining section determines the first value in a period before the signal level of the AC component of the pressure signal detected by the successively determined target element during the increase reaches the maximum value.

In the disclosed pulse wave detecting device, the rotation angle determining section controls the second rotation angle to an arbitrary value in a state where the sensor section is pressed against the body surface, performs, by plural times each with a value of the second rotation angle changed, processing for obtaining a DC component signal group including the DC components of the pressure signals detected by the plurality of pressure detecting elements included in the selected element row in a state where the second rotation angle is controlled to the arbitrary value, and determines, as the second value, a value of the second rotation angle with which a DC component signal group having minimum signal level variation among a plurality of DC component signal groups obtained through the plural times of the processing is obtained.

In the disclosed pulse wave detecting device, the rotation angle determining section determines, based on the DC component signal groups obtained through the processing, a value to be excluded from candidates of the second value out of all possible values of the second rotation angle, and omits to perform the processing with respect to the value to be excluded.

In the disclosed pulse wave detecting device, the rotation angle determining section waits, in the processing, for a prescribed period of time after controlling the second rotation angle to the arbitrary value, and obtains a DC component signal group including the DC components of the pressure signals detected by the plurality of pressure detecting elements included in the selected element row after elapse of the prescribed period of time.

A vital information measuring device herein disclosed includes: the pulse wave detecting device; and a vital information calculating section that calculates vital information based on the pressure signals stored in the storage medium.

A method for controlling a pulse wave detecting device herein disclosed is a method for controlling a pulse wave detecting device including: a sensor section in which a plurality of element rows each including a plurality of pressure detecting elements arranged in a first direction are arranged in a direction perpendicular to the first direction; a pressing section that presses the sensor section against a body surface of a living body in a state where the first direction crosses a direction of extending an artery below the body surface; and a rotation drive section that rotates the sensor section about each of two axes perpendicular to a pressing direction of the pressing section, the two axes being a first axis extending in the first direction and a second axis perpendicular to the first direction, and the method includes: a storage control step of storing, in a storage medium, pressure signals detected by the pressure detecting elements in a state where a first rotation angle of the sensor section about the first axis is controlled to a first value, a second rotation angle of the sensor section about the second axis is controlled to a second value, and the sensor section is pressed against the body surface by the pressing section; and a rotation angle determining step of determining the first value based on the pressure signals detected by the pressure detecting elements during increase of a pressing force applied to the sensor section against the body surface by the pressing section, controlling the first rotation angle to the determined first value using the rotation drive section, and determining the second value based on DC components of the pressure signals detected by the pressure detecting elements in a state where the pressing force is further increased from the thus controlled state.

A control program for a pulse wave detecting device herein disclosed is a control program for a pulse wave detecting device including: a sensor section in which a plurality of element rows each including a plurality of pressure detecting elements arranged in a first direction are arranged in a direction perpendicular to the first direction; a pressing section that presses the sensor section against a body surface of a living body in a state where the first direction crosses a direction of extending an artery below the body surface; and a rotation drive section that rotates the sensor section about each of two axes perpendicular to a pressing direction of the pressing section, the two axes being a first axis extending in the first direction and a second axis perpendicular to the first direction, and the program causes a computer to execute: a storage control step of storing, in a storage medium, pressure signals detected by the pressure detecting elements in a state where a first rotation angle of the sensor section about the first axis is controlled to a first value, a second rotation angle of the sensor section about the second axis is controlled to a second value, and the sensor section is pressed against the body surface by the pressing section; and a rotation angle determining step of determining the first value based on the pressure signals detected by the pressure detecting elements during increase of a pressing force applied to the sensor section against the body surface by the pressing section, controlling the first rotation angle to the determined first value using the rotation drive section, and determining the second value based on DC components of the pressure signals detected by the pressure detecting elements in a state where the pressing force is further increased from the thus controlled state.

The present invention is highly conveniently and effectively applied to a sphygmomanometer in particular.

According to the present invention, a pulse wave detecting device capable improving pulse wave detection accuracy by flexibly changing a pressing state, toward a body surface, of a sensor section pressed against the body surface for use, a vital information measuring device, a control method for a pulse wave detecting device, and a control program for a pulse wave detecting device can be provided.

The present invention has been described so far with reference to a specific embodiment, and it is noted that the present invention is not limited to the embodiment but can be variously modified without departing from the technical spirit of the present invention disclosed herein. 

What is claimed is:
 1. A pulse wave detecting device, comprising: a sensor section in which a plurality of element rows, each including a plurality of pressure detecting elements arranged in a first direction, are arranged in a direction perpendicular to the first direction; an actuator configured to drive the sensor section in a pressing direction of the actuator and to press the sensor section against a body surface in a state where the first direction crosses a direction of an artery extending below the body surface; a rotation drive section that rotates the sensor section about each of two axes perpendicular to the pressing direction of the actuator, the two axes being a first axis extending in the first direction and a second axis perpendicular to the first direction; a storage control section that stores, in a storage medium, pressure signals detected by the pressure detecting elements in a state where a first rotation angle of the sensor section about the first axis is controlled to a first value, a second rotation angle of the sensor section about the second axis is controlled to a second value, and the sensor section is pressed against the body surface by the actuator; and a rotation angle determining section that determines the first value based on the pressure signals detected by the pressure detecting elements during an increase of a pressing force applied to the sensor section against the body surface by the actuator, controls the first rotation angle to the determined first value using the rotation drive section, and determines the second value based on DC components of the pressure signals detected by the pressure detecting elements in a state where the pressing force is further increased from a state where the first rotation angle is controlled to the determined first value.
 2. The pulse wave detecting device according to claim 1, wherein the rotation angle determining section determines the first value based on the pressure signals detected by the plurality of pressure detecting elements included in each of the plurality of element rows.
 3. The pulse wave detecting device according to claim 2, wherein the rotation angle determining section determines the second value based on the DC components of the pressure signals detected by the plurality of pressure detecting elements included in a selected element row corresponding to one element row selected from the plurality of element rows.
 4. The pulse wave detecting device according to claim 1, wherein the rotation angle determining section determines the second value based on the DC components of the pressure signals detected by the plurality of pressure detecting elements included in a selected element row corresponding to one element row selected from the plurality of element rows.
 5. The pulse wave detecting device according to claim 4, wherein the rotation angle determining section performs processing for repeatedly determining, as a target element, during the increase of the pressing force, one element positioned above the artery out of the pressure detecting elements included in the element rows based on a pressure signal group detected by the pressure detecting elements of the element rows, and selects, as the selected element row among the plurality of element rows, an element row having a shortest elapsed time from a start of the increase to a time when a signal level of an AC component of a pressure signal detected by the repeatedly determined target element reaches, after reaching a maximum value, a threshold value specified with reference to the maximum value and smaller than the maximum value.
 6. The pulse wave detecting device according to claim 5, wherein the rotation angle determining section determines the second value in a state where the sensor section is pressed against the body surface with the pressing force applied at the time when the signal level of the AC component of the pressure signal detected by the target element of the selected element row reaches the threshold value.
 7. The pulse wave detecting device according to claim 5, wherein the rotation angle determining section determines the first value in a period before the signal level of the AC component of the pressure signal detected by the repeatedly determined target element during the increase reaches the maximum value.
 8. The pulse wave detecting device according to claim 4, wherein the rotation angle determining section performs processing for repeatedly determining, as a target element, during the increase of the pressing force, one element positioned above the artery out of the pressure detecting elements included in the selected element row based on a pressure signal group detected by the pressure detecting elements of the selected element row, and determines the second value in a state where the sensor section is pressed against the body surface with a pressing force larger than the pressing force applied at a time when a signal level of an AC component of a pressure signal detected by the repeatedly determined target element reaches a maximum value.
 9. The pulse wave detecting device according to claim 4, wherein the rotation angle determining section controls the second rotation angle to an arbitrary value in a state where the sensor section is pressed against the body surface, performs, by plural times each with a value of the second rotation angle changed, processing for obtaining a DC component signal group including the DC components of the pressure signals detected by the plurality of pressure detecting elements included in the selected element row in a state where the second rotation angle is controlled to the arbitrary value, and determines, as the second value, a value of the second rotation angle with which a DC component signal group having minimum signal level variation among a plurality of DC component signal groups obtained through the plural times of the processing is obtained.
 10. The pulse wave detecting device according to claim 9, wherein the rotation angle determining section determines, based on the DC component signal groups obtained through the processing, a value to be excluded from candidates of the second value out of all possible values of the second rotation angle, and does not perform the processing for obtaining the DC component signal group at the value of the second rotation angle to be excluded.
 11. The pulse wave detecting device according to claim 9, wherein the rotation angle determining section waits, in the processing, for a prescribed period of time after controlling the second rotation angle to the arbitrary value, and obtains the DC component signal group including the DC components of the pressure signals detected by the plurality of pressure detecting elements included in the selected element row after elapse of the prescribed period of time.
 12. A vital information measuring device, comprising: the pulse wave detecting device according to claim 1; and a vital information calculating section that calculates vital information based on the pressure signals stored in the storage medium.
 13. A method for controlling a pulse wave detecting device, the pulse wave detecting device including: a sensor section in which a plurality of element rows, each including a plurality of pressure detecting elements arranged in a first direction, are arranged in a direction perpendicular to the first direction; an actuator configured to drive the sensor section in a pressing direction of the actuator and to press the sensor section against a body surface in a state where the first direction crosses a direction of an artery extending below the body surface; and a rotation drive section that rotates the sensor section about each of two axes perpendicular to the pressing direction of the actuator, the two axes being a first axis extending in the first direction and a second axis perpendicular to the first direction, the method comprising: a storage control step of storing, in a storage medium, pressure signals detected by the pressure detecting elements in a state where a first rotation angle of the sensor section about the first axis is controlled to a first value, a second rotation angle of the sensor section about the second axis is controlled to a second value, and the sensor section is pressed against the body surface by the actuator; and a rotation angle determining step of determining the first value based on the pressure signals detected by the pressure detecting elements during an increase of a pressing force applied to the sensor section against the body surface by the actuator, controlling the first rotation angle to the determined first value using the rotation drive section, and determining the second value based on DC components of the pressure signals detected by the pressure detecting elements in a state where the pressing force is further increased from a state where the first rotation angle is controlled to the determined first value.
 14. A non-transitory computer-readable storage medium, which stores a control program for a pulse wave detecting device, the pulse wave detecting device including: a sensor section in which a plurality of element rows, each including a plurality of pressure detecting elements arranged in a first direction, are arranged in a direction perpendicular to the first direction; an actuator configured to drive the sensor section in a pressing direction of the actuator and to press the sensor section against a body surface in a state where the first direction crosses a direction of an artery extending below the body surface; and a rotation drive section that rotates the sensor section about each of two axes perpendicular to the pressing direction of the actuator, the two axes being a first axis extending in the first direction and a second axis perpendicular to the first direction, the program causing a computer to execute: a storage control step of storing, in a memory, pressure signals detected by the pressure detecting elements in a state where a first rotation angle of the sensor section about the first axis is controlled to a first value, a second rotation angle of the sensor section about the second axis is controlled to a second value, and the sensor section is pressed against the body surface by the actuator; and a rotation angle determining step of determining the first value based on the pressure signals detected by the pressure detecting elements during an increase of a pressing force applied to the sensor section against the body surface by the actuator, controlling the first rotation angle to the determined first value using the rotation drive section, and determining the second value based on DC components of the pressure signals detected by the pressure detecting elements in a state where the pressing force is further increased from a state where the first rotation angle is controlled to the determined first value. 